Velocity monitor for aircraft

ABSTRACT

This invention pertains to a velocity monitor for an aircraft wherein a signal is given if, during the ground-roll of a takeoff, the actual velocity falls below that necessary for successful take-off. To this end there is provided in series connection an accelerometer, a first and a second integrator, a function generator and a comparator for the first integral being a signal of actual velocity and the output of the function generator being a signal of desired velocity. The output of the comparator shows whether actual velocity is above or below the desired velocity.

United States Patent [191' Pollitt 1111 3,709,033 1 1 Jan. 9, 1973 [54]VELOCITY MONITOR FOR AIRCRAFT [75] Inventor: James Pollitt, Bristol,England 73] Assignee: Rolls-Royce Limited, Derby, En-

' gland 221 Filed: on. 19, 1970 21 Appl; No.: 82,052

[30] Foreign Application Priority Date Oct. 21, 1969 Great Britain..5l,5l0/69 52] U.S. Cl. .Q ..13/17s r 51 110.01; ..G0lc 21/10 [58]Field of Search ..'.....-....-..-.73/17s T, 178 R, 490

[561' References Cited 7 UNITED STATES PATENTS 3,034,096 5/1962 Craddock..'....73/178 T Primary Examiner-Donald O. Woodiel Attorney-Stevens,Davis, Miller & Mosher [57] 1 ABSTRACT This invention pertains to avelocity monitor for an aircraft wherein a signal is given if, duringthe groundroll of a take-off, the actual velocity falls below thatnecessary for successful take-off. To this end there is provided inseries connection an accelerometer, a first and a second integrator, afunction generator and a comparator for the firstintegral being asignal-of actual velocity and the output of the function generator beinga signal of desired velocity. The output .of the comparator showswhether actual velocity is above or below the desired velocity.

, 4 Claims, 2 Drawing Figures IACCELEFQOMETER,v

2/1963 Gold ..73/1 78 T PATENTEDJAH 9 I975 SHEET 1 [IF 2 INVENTOR JAMESPOLLITT 'ZmMMW M ATTORNEYS 1 VELOCITY MONITOR FOR AIRCRAFT Thisinvention relates to a velocity monitor for aircraft.

It is an object of this invention to provide apparatus whereby it ispossible, at the beginning or during the ground-roll of a take-off, todetermine whether the velocity necessary for becoming airborne can beattained within a given distance along the runway.

According to this invention there is provided apparatus for monitoringthe velocity of an aircraft, comprising means capable of cooperatingwith the aircraft for producing a first velocity signal indicative ofthe actual velocity of the aircraft, means capable of cooperating withthe aircraft for producing a signal indicative of the distance travelledby the, aircraft, means for deriving a second velocity signal being apre-determined function of the distance signal, means for varying themean slope of said function to produce a modified function signal, andmeans for comparing the first velocity signal and the modified functionsignal to produce an output indicative of the relative superiority ofthe compared signals.

Said function is a pre-determined basic relationship between velocityand distance travelled if the aircraft is to be able to complete astandard take-off. Said means for varying the mean slope of the functionmake it possible to allow for changing parameters such as aircraft loador available length of runway.

Preferably said mean slope is determined as a function of theinitialacceleration necessary for a safe takeoff, and to this end the apparatusmay comprise an accelerometer, an instrument for thedisplay ofacceleration including two independently moveable indicators, means fordriving one of the indicators in response to the output of theaccelerometer, and means for setting the other indicator connected tosaid means for varying the slope of said function for the latter slopeto be variable in response to actuation of the setting means.

An exampleof apparatus according to this invention, as applied to anaircraft take-off maneuver, will now be described with reference to theaccompanying drawings wherein:

FIG. 1 is a diagram of an electrical circuit of the apparatus and FIG. 2is a set of curves showing different velocity/distance relationships inrespect to an aircraft take-off.

Referring to the drawings, there is shown an accelerometer known per seand having an electrical output 11 in terms of millivolts/unit ofacceleration. Theaccelerorneter is installed in an aircraft A to sensethe acceleration thereof. The signal 1 l is connected to an electricalanalogue computer 12 in which this signal is connected to a firstintegrator 13 to produce an output 14 being at any one time the velocityattained by the aircraft in consequence of the acceleration. The signal14 is connected to a second integrator 15 to produce an output 16 beingat any one time the distance travelled by the aircraft in consequence ofthe acceleration. The signal 16 is connected to a function generator 17adapted to produce a signal 18 defining a velocity whichthe aircraftwould attain at any given distance travelled during a typical take-off.

The signal 18 is also referred to as the basic take-off law. This law,which depends on such substantially constant factors as engine behaviorand aircraft aerodynamics, is originally determined experimentally byperforming a typical take-off mission at full engine power with astandard load and under as near standard atmospheric conditions aspossible. Minor adjustments are then made by calculation, to establishthe law as it would be on a standar day. The function generator. 17 isthen constructed to reproduce this basic take-off law in the form of thesignal 18. I

FIG. 2 shows the law 18 as plottedbetween the start of the take-off run,signified by S0, and a distance S1 at which the aircraft has attained avelocity V1 at which the take-off can be completed safely. if thevelocity V1 is not attained at position S1 then the take-off must beabandoned. The distance S1 allows for sufficient runway to be availablefor the aircraft to be halted safely if the take-off is abandoned.

The function generator 17 comprises a plurality of amplifiers 19 to 22having progressively higher threshold voltages so that as the distancesignal 16 rises from zero to S1 the amplifiers are sequentially broughtinto use. The gains of the successive amplifiers are adjusted so thattheir outputs 23 define successive portions of the law. 18. The outputs23 are fed to a highest gain unit 24 which allows only the highest ofthe signals to pass, and the output of the unit 24 constitutes the law18. The gains of the amplifiers 19 to 22 are linear and it is assumedherein that the law 18 can be represented by a succession of linearfunctions.

The means slope of the law 18 varies with certain environmentalparameters, for example the length of the runway. Thus, if a longerrunway is available the distance necessary to attain V1 maybe increased.Assuming full power is used again, the longer runway will permit anincrease in take-off weight but at' reduced acceleration. Generally, themean slope'of the law i8 is a function of the acceleration required tocarry out a particular take-off mission. p

It has been found that said mean slope is in fact determined, at leastto a good approximation, by the acceleration required at thecommencement of the take-off run. This initial acceleration can becalculated or taken from charts.

To change the slope of the signal 18 in accordance with said initialacceleration, the signal 18 is fed to an amplifier 25 provided with apotentiometer 26 connect'ed to vary the gain of this amplifierfTheoutput, denoted 27, of the amplifier 25 is therefore proportional to thelaw 18 but at a mean slope depending on the setting of the potentiometer26. The signal 27 is also referred to as the modified law."

The potentiometer 26 is settable by means of a knob 28 provided on adial instrument 29 embodying a marker or indicator 30 connected to berotated by the knob 28 relative to a scale 31. The instrument 29includes an indicator 32 adapted to be driven relative to the scale 31by the signal 11 for direct display of acceleration. Means for drivingan indicator such as 32 from an electrical signal are sufficientlyindicated by an amplifier 45 as such means are well known per se.

It will be seen from FIG. 2 that, for constant maximum velocity, themean slope of the function is proportional to the distance travelled andproportional to the initial acceleration. There is, therefore, noincompatibility between a reading of acceleration being used for settingsaid slope.

The purpose of producing the modified law 27 is to make it possible tomonitor the ground roll to see whether actual velocity matches thatrequired by the law 27. To this end the velocity signal 14 and thesignal 27 are fed to a comparator network 33 adapted to produce a signal34 whose sign changes with the sign of the sum of the two signals 14,27. The signal 34 is fed to a pair of lamps 35,36 through diodes 37,38such that the lamp 35 lights when the signal 14 is greater than thesignal 27 to indicate that take-off can proceed normally, or that thelamp 36 light to indicate that actual velocity is below the safe limitset by the law 27 in the latter case the pilot will abandon thetake-off.

The action defining the commencement of the ground roll is usually therelease of the ground wheel brakes of the aircraft. This is actuated bymeans of a switch 39. During the first moments of the ground roll theaccelerometer reading may be inaccurate due to possible pitching of theaircraft following the release of the brakes. To prevent the lamp 36lighting under these circumstances the signal 34 is led through anAND-gate 40 together with a signal 41 being the output of a delay unit42 whose action is initiated by a set of contacts 43 of the switch 39.Thus when the switch 39 is operated the lamps 35,36 are disconnecteduntil the delay unit produces its output. During this delay period thepointer 32 provides an instant indication of whether actual accelerationmeets that set by the marker 30. First, quite apart from said delay, thepilot can see directly from the dial 29, and independently of thecomputer 12 whether the take-off is likely to succeed, and during theremainder of the take-off the lamps 35,36 will indicate to the pilotwhether the success condition is being maintained.

The use of acceleration as the parameter determining the slope of thebasic law is of particular advantage because this is directlyrepresentative of the aircraft performance required for the mission. Itwould, for example, not be as useful to take engine power as thedetermining parameter although the power is proportional toacceleration. The reason is that even if engine power can be measuredaccurately, and this can be difficult, it would still be possible to getunrealistic results because power could be exerted without necessarilyaffecting velocity as in the case of faulty brakes or slush on therunway or any other unpredicted condition of resistance to movement.

In the foregoing description it has been assumed that the take-offmission will be carried out at full power and that the modified law isindicative of the performance which has to be achieved using full power.As a result, when take-off conditions are not limiting, e.g., at lightweights or ample length of runway, full power is used unnecessarily.

To avoid this, the acceleration value fed to the computer may be thatcorresponding to the least power which is safely required for take-off.This required minimum acceleration is also calculated or taken fromcharts, but including a margin of safety. The pilot will set the engineto a given power setting, usually in terms of engine speed or overallengine pressure ratio in the case of jet engines, or torque in the caseof a propellor power plant, and will monitor his instruments to maintainthat power setting. The power requirement can, of course, be fed into anautomatic closed loop control system to maintain power automatically.

The visual display by the lamps 35,36 may have means to display thelegends GO-and STOP depending on whether the actual velocity is above orbelow the safe one.

The system may include an air speed sensor (not shown) connectedadjacent the lamps 35,36 so that when a certain preselected airspeed,that is the velocity V1, is attained, the legend V1 appears on thedisplay to the exclusion of the legends G0 and *STOP." The pilot willthen know that he can end the actual take-off run or ground roll andlift the aircraft off the runway.

We claim:

1. Apparatus for monitoring the velocity of an aircraft comprising meanscapable of cooperating with the aircraft for producing a first velocitysignal indicative of the actual velocity of the vehicle, means capableof cooperating with the vehicle for producing a signal indicative of thedistance travelled by the vehicle, means for deriving a second velocitysignal which is a predetermined function of the distance signal and hasa mean slope, means for varying the mean slope of said function toproduce a modified function signal, means for comparing the firstvelocity signal and the modified function signal to produce an outputindicative of the relative superiority of the compared signals, anaccelerometer, an instrument for the display of acceleration includingtwo independently movable indicators, means for driving one of theindicators in response to the output of the accelerometer, and means forsetting the other indicator connected to said means for varying the meanslope of said function to make the latter indicator variable in responseto actuation of the setting means.

2. Apparatus for monitoring the velocity of an aircraft comprising inseries connection an accelerometer,

a first integrator, a second integrator, a function generator forgenerating a predetermined function having a means slope, and manuallyoperable means for varying the mean slope of the output of the functiongenerator; and further comprising a comparator having as its inputs theoutput of the first integrator and the output of the manually operablemeans, a display means connected to the comparator for showing whicheverof the two comparator inputs is the greater, a display means for theoutput of the accelerometer, a scale of acceleration included in thelatter means, and the manual means being arranged to be settable againstsaid scale.

3. Apparatus for monitoring the velocity of an aircraft during groundroll comprising first integrating means capable of cooperating with anaccelerometer in said aircraft for producing a first velocity signalcorresponding to the actual instantaneous velocity of the aircraft;second integrating means coupled to the output of said first integratingmeans for producing a signal corresponding to the actual instantaneousdistance travelled by said aircraft during ground roll; functiongenerator means having its input coupled only to the output of saidsecond integrating means for producing a second velocity signal which isa predetermined increasing function of the actual instantaneous distancetravelled by said aircraft, said predetermined function having a meanpositive slope; means for varying the mean slope of said predeterminedfunction as an approximate function of the acceleration required at thecommencement of the take-off run to produce a modified function signalcorresponding to the desired velocity of said aircraft;.and means forcomparing the first velocity signal and the modified function signal toproduce an output indicative of the actual instantaneous velocity of theaircraft as compared to the desired velocity.

4. The method of monitoring the velocity of an aircraft duringground-roll prior to take-off comprising the steps of a. determining theinitial acceleration required at the commencement of the ground-roll toattain said take-off velocity and setting a function modifier inaccordance with said initial acceleration,

b. determining the actual instantaneous acceleration of said aircraftduring ground-roll,

c. displaying the initial acceleration required at the commencement ofground-roll to attain safe takeoff velocity and the actual instantaneousacceleration of said aircraft,

d. determining the actual instantaneous velocity of said aircraft duringground-roll,

e. determining at each instant the distance travelled by said aircraftduring ground-roll,

f. generating a predetermined velocity function varying substantiallywith the distance travelled during ground-roll by said aircraft, saidpredetermined velocity function having a mean slope,

g. modifying the mean slope of said predetermined velocity function inaccordance with said initial acceleration required for a safe take-offto produce a modified velocity function,

h. comparing the instantaneous velocity of said aircraft with saidmodified velocity function, and

i. indicating whether the instantaneous velocity is less than themodified velocity function, as instantaneous velocity less than themodified velocity function being unsafe for take-off.

1. Apparatus for monitoring the velocity of an aircraft comprising meanscapable of cooperating with the aircraft for producing a first velocitysignal indicAtive of the actual velocity of the vehicle, means capableof cooperating with the vehicle for producing a signal indicative of thedistance travelled by the vehicle, means for deriving a second velocitysignal which is a predetermined function of the distance signal and hasa mean slope, means for varying the mean slope of said function toproduce a modified function signal, means for comparing the firstvelocity signal and the modified function signal to produce an outputindicative of the relative superiority of the compared signals, anaccelerometer, an instrument for the display of acceleration includingtwo independently movable indicators, means for driving one of theindicators in response to the output of the accelerometer, and means forsetting the other indicator connected to said means for varying the meanslope of said function to make the latter indicator variable in responseto actuation of the setting means.
 2. Apparatus for monitoring thevelocity of an aircraft comprising in series connection anaccelerometer, a first integrator, a second integrator, a functiongenerator for generating a predetermined function having a means slope,and manually operable means for varying the mean slope of the output ofthe function generator; and further comprising a comparator having asits inputs the output of the first integrator and the output of themanually operable means, a display means connected to the comparator forshowing whichever of the two comparator inputs is the greater, a displaymeans for the output of the accelerometer, a scale of accelerationincluded in the latter means, and the manual means being arranged to besettable against said scale.
 3. Apparatus for monitoring the velocity ofan aircraft during ground roll comprising first integrating meanscapable of cooperating with an accelerometer in said aircraft forproducing a first velocity signal corresponding to the actualinstantaneous velocity of the aircraft; second integrating means coupledto the output of said first integrating means for producing a signalcorresponding to the actual instantaneous distance travelled by saidaircraft during ground roll; function generator means having its inputcoupled only to the output of said second integrating means forproducing a second velocity signal which is a predetermined increasingfunction of the actual instantaneous distance travelled by saidaircraft, said predetermined function having a mean positive slope;means for varying the mean slope of said predetermined function as anapproximate function of the acceleration required at the commencement ofthe take-off run to produce a modified function signal corresponding tothe desired velocity of said aircraft; and means for comparing the firstvelocity signal and the modified function signal to produce an outputindicative of the actual instantaneous velocity of the aircraft ascompared to the desired velocity.
 4. The method of monitoring thevelocity of an aircraft during ground-roll prior to take-off comprisingthe steps of a. determining the initial acceleration required at thecommencement of the ground-roll to attain said take-off velocity andsetting a function modifier in accordance with said initialacceleration, b. determining the actual instantaneous acceleration ofsaid aircraft during ground-roll, c. displaying the initial accelerationrequired at the commencement of ground-roll to attain safe take-offvelocity and the actual instantaneous acceleration of said aircraft, d.determining the actual instantaneous velocity of said aircraft duringground-roll, e. determining at each instant the distance travelled bysaid aircraft during ground-roll, f. generating a predetermined velocityfunction varying substantially with the distance travelled duringground-roll by said aircraft, said predetermined velocity functionhaving a mean slope, g. modifying the mean slope of said predeterminedvelocity function in accordance with said initial acceleration reQuiredfor a safe take-off to produce a modified velocity function, h.comparing the instantaneous velocity of said aircraft with said modifiedvelocity function, and i. indicating whether the instantaneous velocityis less than the modified velocity function, as instantaneous velocityless than the modified velocity function being unsafe for take-off.